Abstract: An exhaust valve assembly comprises a housing having a central axis. A ram assembly moves along a shaft fixed inside a hollow interior of the housing. Downstream movement of the ram assembly increases the size of the valve opening, allowing additional exhaust gases to pass through the interior of the housing. Springs maintain the ram assembly in a position in which exhaust gases may pass around the ram assembly. Sufficient force on the ram assembly from exhaust gases compresses at least one spring allowing the ram assembly to move downstream, thereby allowing additional exhaust gases to pass through the interior of the housing.

Abstract: An exhaust system for a marine engine comprising liquid cooled manifold and catalytic converter assemblies. Each assembly uses a separate cooling system to cool either the exhaust manifold or a shell inside which resides the catalytic converter. The housing or shell containing the catalytic converter uses water to cool an exterior surface of a water jacket to an acceptable temperature conforming to federal regulations. The liquid-cooled manifold assembly may use either water or glycol to cool a jacket surrounding tubes extending from the engine block to the catalytic converter assembly.